1. Field of the Invention
The present invention relates to an apparatus for reproducing an information signal from a multiplicity of parallel tracks formed on a recording medium and, more particularly, to tracking control suitable for use in a so-called helical scan type of magnetic video recording and reproducing apparatus (hereinafter referred to as the "VTR").
2. Description of the Related Art
VTRs which are widely known as this kind of VTR include domestic-use VTRs which conform to the VHS system, the 8 mm video system or the like. Various methods for controlling head tracking during reproduction in such a VTR are proposed and practiced to faithfully trace recorded video tracks during reproduction. In the VHS system, timing pulse signals are recorded along the bottom end of a tape in correspondence with track positions (CTL system). In the 8 mm video system, a video signal onto which each of pilot signals of four different frequencies is multiplexed is recorded on each track (4f system).
In the field of domestic-use VTRs, to cope with a demand for a further improvement in image quality and a technical trend toward digitization, a VTR has recently been developed which is arranged to record an image signal for one field divisionally over a plurality of tracks so that a comparatively large amount of information can be recorded and reproduced. In addition, the following methods are proposed as tracking control systems suitable for use in digital information recording.
When a digital signal to be recorded is to be modulated, a recording signal is formed so that a frequency component corresponding to a particular pilot signal can be contained in a modulated signal, and a tracking controlling pilot signal is multiplexed with a digital information signal through the modulation of the digital signal.
More specifically, it is proposed to multiplex each of pilot signals onto each associated track, as shown in FIG. 2, in a VTR having the head arrangement shown in FIG. 1. FIG. 1 shows the positional relationships between two heads A and B, a rotary head drum 100 and a magnetic tape 101.
The operation of the shown example will be described below. In the track pattern shown in FIG. 2 which is recorded on the tape 101 by the heads A and B having different azimuth angles as shown in FIG. 1, pilot signals f.sub.1 and f.sub.2 of different frequencies are alternately recorded on the tracks to be recorded by the head B in the state of being multiplexed with a video information signal. As a multiplexing method, it is possible to utilize a method of selecting the frequency of the pilot signal f.sub.1 or f.sub.2 from a frequency band different from that of a video information signal and multiplexing either of the pilot signals f.sub.1 or f.sub.2 at the selected frequency, or it is also possible to utilize a method of carrying out modulation in such a manner as to control the digital sum value of a digital signal to be recorded, so that frequency spectra f.sub.1 and f.sub.2 can be obtained by reproduction. Incidentally, in FIG. 2, symbols "f.sub.0 " indicate tracks on which neither of the pilot signals f.sub.1 and f.sub.2 is multiplexed with the video information signal.
During reproduction, by comparing an f.sub.1 component and an f.sub.2 component which are contained in a signal reproduced by the head A tracing each of the tracks shown by f.sub.0 in FIG. 2, it is possible to detect to what extent and to which side the position of head tracing is shifted. The resultant output can be used as a tracking error signal.
In the above-described example, however, the level of a tracking control signal which is obtained when the heads A and B are shifted by two tracks is substantially equal to the level of a tracking control signal which is obtained when the heads A and B are not shifted. Therefore, for example, if the running of the tape 101 starts to delay from the tracing of the heads A and B, the level of a tracking control signal becomes lower in spite of the occurrence of the delay in the running of the tape 101. As a result, the running of the tape 101 further delays and a shift for two tracks is cancelled, so that a normal tracking state is recovered. However, a considerably long time is required to recover the normal tracking state, and, during this time, since an off-track state is necessarily involved, no reproduced signal is obtained due to an azimuth loss, so that a visually impaired image is reproduced.
Particularly if tracking is shifted for two tracks when head tracing transfers from a non-recorded portion to a recorded portion during reproduction, a state similar to the aforesaid one occurs, and the time during which a reproduced image is disturbed until the tracking recovers a normal state becomes long. A similar phenomenon also occurs immediately after the mode of reproduction transfers from what is called "cue.review" (fast forward feeding reproduction or fast backward feeding reproduction) to normal reproduction.